Biology Reference
In-Depth Information
anti-infl ammatory and antibacterial chemotherapy have dramatically improved the life
span of the CF population, albeit pathogenic resistance to commonly used antibiotics
has raised the demand for the development of novel therapeutic modalities [11-13].
Antibiotics like aminoglycosides and polymyxins have been used for the treatment
of acute or chronic exacerbations in response to multi-drug resistant (MDR) bacteria,
particularly Gram-negative bacilli such as
P. aeruginosa
[14-17]. Aminoglycosides
including tobramycin contain broad antibacterial and post-antibiotic effect, but due to
their hydrophilic nature, they are not absorbed and have adverse effects (i.e., nephro-
toxicity, ototoxicity) when parenterally administered [17-19]. Presently, intravenous
administration of aminoglycosides is widely used by CF clinicians and limiting the
dose to daily administration seems to reduce adverse effects [20, 21]. Polymyxins
are cationic polypeptides that bind to lipopolysaccharide of the Gram-negative bacte-
ria and increase their membrane permeability and cell death. Cytotoxicity issues and
adaptive resistance by bacterial cell surface alterations have limited their application
to cases where other antibiotics have failed [22-24].
Clinical studies have shown the success of antibiotics used in inhalation therapy,
alone or in synergism, to combat MDR
P. aeruginosa
[25-31]. However, loss of innate
immune response, the emergence of resistant mucoidal strains, and increase in biofi lm
production, and the buildup of thick polyanionic sputum have hampered complete
eradication of these infections [7,32-35]. Although an antibiotic may display activ-
ity against planktonic bacteria
in vitro
, the harsh environment of sputum containing
factors produced by host and the microbes reduce their potential interactions with the
targeted pathogens [36, 37]. Clinical experiments have shown that in the presence of
sputum, antibiotic potency is reduced mainly because of binding to sputum and its
inhibitory components like glycoproteins [e.g., mucin (8-47 mg/ml)] [38], neutrophil
derived DNA (0.6-6.6 mg/ml) [38], and actin fi laments (0.1-5 mg/ml) [39], and bacte-
rial endotoxins such as LPS and LTA [40-47].
Liposomes are biodegradable delivery vesicles made up of single or multiple phos-
pholipids in the range of several nanometers to micrometers [48, 49]. It is clear that
entrapment of the majority of antibacterial agents in liposomes tends to enhance bio-
activity, bioavailability, and lower drug toxicity [50-52]. Liposomes may protect the
entrapped agent from aggregation and inactivation with polyanionic components of
the CF sputum, hence increasing its activity at the site, although the sputum may act
as a barrier to larger liposomes [53-55]The present study was carried out to answer the
following questions: (i) Are liposome-entrapped antibiotics stable in the environment
of the sputum? (ii) Will the entrapment within liposomes reduce antibiotic interac-
tion with the inhibitory factors present in the sputum? (iii) Will liposome-entrapped
antibiotics reduce the number of live bacteria in sputum more effectively than the free
antibiotics?
Our data demonstrate that liposomes are stable in presence of sputum and inhibi-
tory factors. This data is encouraging as it displays the ability of lipid vesicles to
protect the antibiotics from inactivation. The study shows that free tobramycin and
polymyxin B, incubated with negatively charged inhibitory factors, is greatly inhibited
compared to liposome-entrapped forms at higher concentrations. Liposome-entrapped
